Clearly display names for .Net Framework

[svick]

This changes the display for CsProjClassicNetToolchain, so that it properly shows the framework name, instead of just the TFM.

E.g. consider this benchmark:

[Config(typeof(Config))]
public unsafe class Toolchain
{
    private class Config : ManualConfig
    {
        public Config()
        {
            AddJob(Job.Default.WithToolchain(CsProjClassicNetToolchain.Net48));
            AddJob(Job.Default.WithToolchain(CsProjCoreToolchain.NetCoreApp31));
        }
    }

    [Benchmark]
    public void Sleep() => Thread.Sleep(1);
}

Before this change, its output is (notice the Toolchain column in the table):

// * Summary *

BenchmarkDotNet=v0.12.1.20200610-develop, OS=Windows 10.0.18362.836 (1903/May2019Update/19H1)
Intel Core i5-2300 CPU 2.80GHz (Sandy Bridge), 1 CPU, 4 logical and 4 physical cores
  [Host]     : .NET Framework 4.8 (4.8.4180.0), X64 RyuJIT
  Job-UPLABW : .NET Core 3.1.5 (CoreCLR 4.700.20.26901, CoreFX 4.700.20.27001), X64 RyuJIT
  Job-JBFOWH : .NET Framework 4.8 (4.8.4180.0), X64 RyuJIT


| Method |        Job |     Toolchain |     Mean |     Error |    StdDev |
|------- |----------- |-------------- |---------:|----------:|----------:|
|  Sleep | Job-UPLABW | .NET Core 3.1 | 1.808 ms | 0.0332 ms | 0.0310 ms |
|  Sleep | Job-JBFOWH |         net48 | 1.783 ms | 0.0350 ms | 0.0612 ms |

After it, it's instead:

// * Summary *

BenchmarkDotNet=v0.12.1.20200610-develop, OS=Windows 10.0.18362.836 (1903/May2019Update/19H1)
Intel Core i5-2300 CPU 2.80GHz (Sandy Bridge), 1 CPU, 4 logical and 4 physical cores
  [Host]     : .NET Framework 4.8 (4.8.4180.0), X64 RyuJIT
  Job-UPLABW : .NET Core 3.1.5 (CoreCLR 4.700.20.26901, CoreFX 4.700.20.27001), X64 RyuJIT
  Job-RMSQHR : .NET Framework 4.8 (4.8.4180.0), X64 RyuJIT


| Method |        Job |          Toolchain |     Mean |     Error |    StdDev |
|------- |----------- |------------------- |---------:|----------:|----------:|
|  Sleep | Job-UPLABW |      .NET Core 3.1 | 1.762 ms | 0.0351 ms | 0.0444 ms |
|  Sleep | Job-RMSQHR | .NET Framework 4.8 | 1.710 ms | 0.0226 ms | 0.0188 ms |

Also, it changes the name for ClrRuntimes from e.g. ".NET 4.8" to the more correct ".NET Framework 4.8". (Which is especially important to differentiate them from .Net 5.0.)

[adamsitnik]

LGTM, thank you @svick !